In this study we report a randomized double-blind, placebo-controlled trial to evaluate the effect of ORG 2766 in IDDM patients with peripheral neuropathy. Sixty-two patients were selected based on the following criteria: abnormal vibration perception threshold above the 95th-percentile adjusted for age and/or abnormal warm temperature threshold, both measured in the right hand. The patients were randomized into two treatment groups after baseline studies: Group 1 was treated with placebo and Group 2 was treated with 3 mg of the ACTH4-9 analogue ORG 2766 every 24 h. The total study period was 1 year. After 1 year of treatment there was a significant improvement in vibration threshold in Group 1 compared to Group 2. No other parameters improved in the study period. The number of patients selected may have been too small to detect a more important treatment effect. We conclude from this study that ORG 2766 can improve vibration threshold, indicating large myelinated fibre function, but does not affect any of the other neurophysiological function tests.